Researchers at Kaiser Permanente in Portland, Oregon tested the amount of vitamin D in both compounded and 15 different OTC manufactured supplements. The products were randomly selected and analyzed by high performance liquid chromatography to determine their actual potency as compared to the labeled amounts. Researchers found the products ranged from 9-146% of the labeled dose, with only one-third of compounded and just over half of the OTC products meeting USP standards of 90-110% of the expected dose. The manufacturers with labeling that indicated USP verification had the most accurate potency and least variability.How often do you or your patients question the potency standards of vitamins?